Gas turbine apparatus and a starting method thereof

ABSTRACT

A gas turbine starting method, comprising the steps of rotatively driving a turbine by a motor coupled to the turbine, while at the same time supplying a compressed air to a combustor by an air compressor operating in interlocking motion with the turbine, starting a fuel supply to the combustor when a revolution speed of the turbine has reached up to a predetermined value, and simultaneously starting an igniting operation on an air-fuel mixture in the combustor, wherein at least during the igniting operation to the air-fuel mixture in the combustor, a quantity of fuel supply per unit time to the combustor is increased while increasing the revolution speed of the turbine, to thereby ensuring the ignition of the air-fuel mixture under various conditions, and depressing the temperature rise of the gas turbine, which may otherwise occur immediately after the ignition.

FIELD OF THE INVENTION

[0001] The present invention relates to a gas turbine apparatus and astarting method thereof, and in particular, to a starting method forstarting a gas turbine apparatus by using a starting motor.

BACKGROUND OF THE INVENTION

[0002] In general, a gas turbine apparatus basically comprises a turbinemounted on a rotary shaft, a combustor for burning a mixture of fuel andair to generate a combustion gas, a fuel flow control valve forcontrolling a quantity of fuel supply to the combustor, an aircompressor for supplying the combustor with compressed air, the aircompressor operating in interlocking motion with the turbine, and so on.In thus constructed apparatus, the air-fuel mixture produced by means ofthe fuel flow control valve and the air compressor is burnt to generatea combustion gas of high temperature and high pressure, which is thensupplied to the turbine to make it revolve at high speed.

[0003] In this type of gas turbine apparatus, when it is to be started,such a method has been employed in which the turbine is driven by amotor for starting to actuate the gas turbine apparatus. That is, firstof all, the turbine is rotatively driven by the motor while at the sametime the air compressor is driven by the motor via the rotary shaft tostart a supply of the compressed air to the combustor. After that, thefuel flow control valve is opened to supply the combustor with a fuel toproduce a mixture of compressed air and the fuel therein. Subsequently,an igniting operation for the air-fuel mixture is started in thecombustor, and then the air-fuel mixture is burned to generate thecombustion gas, which is supplied to the turbine thereby making theturbine revolve at high speed.

[0004] In this regard, one of the requirements for igniting the air-fuelmixture is an appropriate mass ratio (or weight ratio) of air and fuelin the mixture, or an air fuel ratio (sometimes abbreviated to A/F). Theair fuel ratio is the mass ratio between the air and the fuel, or amixture ratio, provided for the combustion, which may be obtained as aflow rate of the air per unit time divided by a flow rate of the fuelper unit time. As described above, since the air is compressed by thecompressor and then fed to the combustor, and this compressor has beendriven in interlocking motion with the turbine, the flow rate of the aircan be calculated based on a revolution speed of the turbine. On theother hand, the flow rate of the fuel can be calculated based on anopening of the fuel flow control valve. Accordingly, the air fuel ratiocan be determined from the revolution speed of the turbine and theopening of the fuel flow control valve.

[0005]FIG. 5 is a schematic diagram of the revolution speed of theturbine, the opening of the fuel flow control valve and a temperature ofan exhaust gas of the conventional turbine apparatus, each illustratedas a function of an elapsed time during a starting operation thereof. InFIG. 5, NR(Number of Revolution) represents a revolution speed of theturbine, FCV(Fuel Control Valve) represents an opening of the fuel flowcontrol valve, EGT(Exhaust Gas Temperature) represents a temperature ofthe exhaust gas, and MC(Motor Current) represents a quantity of currentsupply per unit time to the motor, respectively.

[0006] As can be seen from FIG. 5, firstly the turbine is rotativelydriven by the motor (see dotted line MC of FIG. 5), and after therevolution speed of the turbine reaches up to the revolution speed NR₁required for ignition, the motor is controlled to maintain saidrevolution speed NR₁. Then, the fuel supply to the combustor is begun toproduce the air-fuel mixture and simultaneously the igniting operationis started (t₁). At this time, the quantity of fuel supply per unit time(the opening of the fuel flow control valve) is maintained, as shown inFIG. 5, to a predetermined level of fuel supply quantity (fcv₁) suitablefor the ignition.

[0007] Then, the air-fuel mixture is ignited to generate the combustiongas (t₂), which is fed to the turbine so as to provide the powerthereto, and thereby the revolution speed of the turbine is increased.Subsequently, the rotatively driving operation of the motor is stopped.When the rotatively driving operation by the combustion gas begins, aspeed up of the turbine is put under the control by adjusting the supplyquantity of the combustion gas to the turbine. That is, a speed upcontrol is applied, in which the opening of the fuel flow control valveis operated to increase the revolution speed of the turbine so that anacceleration of revolution of the turbine may reach up to apredetermined target acceleration level.

[0008] As described above, during the igniting operation (time periodfrom t₁ to t₂), the air fuel ratio is set to be a certain value suitablefor ignition, and accordingly, as shown in FIG. 5, the revolution speedof the turbine (the flow rate of the compressed air) and the opening ofthe fuel flow control valve (the fuel supply quantity) are maintained tobe constant respectively. Thus, the igniting operation is performedunder the specific air fuel ratio suitable for ignition so that theair-fuel mixture may be ignited soon.

[0009] However, the air fuel ratio suitable for ignition variesdepending on the specific actual conditions in respective ignitionoperations. For example, when the temperature of surrounding environmentis low, it is rather difficult to accomplish a smooth ignition, while anignition for restarting under a high temperature condition of the gasturbine main body shortly after the stop of operation may be performedeasily. That is, the ignition may not always be successfully performedunder the same air fuel ratio on every occasion, and sometimes theair-fuel mixture cannot be ignited resulting in a failure of thestarting operation.

[0010] In order to deal with the problem described above, one approachhas been conventionally attempted, in which, as shown in FIG. 6, whilekeeping the revolution speed of the turbine to be constant, the openingof the fuel flow control valve is increased gradually to vary the airfuel ratio so as to follow the change in the suitable ignitioncondition. In this case, however, such a problem has arisen as follows.That is, immediately after the ignition (t₂), as described above, thecontrol of the turbine is switched from the phase of the driving by themotor to another phase of the speed up control by the supply of thecombustion gas. At that time, since the revolution speed of the turbineimmediately after the ignition (t₂) is kept constant and theacceleration thereof is equal to zero, the acceleration of revolution ofthe turbine right after the switching of the control phase has asubstantial deviation from the target acceleration thereof.

[0011] This makes the fuel flow control valve open to excessive degreeright after the shifting to the speed up control phase due to a controlaction needed for minimizing this deviation. Therefore, the fuel isexcessively supplied to the combustor through the fuel flow controlvalve, which cause a problem that immediately after the ignition, thetemperature of the gas turbine apparatus, in particular, of thecombustor thereof rapidly rises up to high temperature (see the exhaustgas temperature of FIG. 6). This problem occurs also in the caseemploying the starting method shown in FIG. 5.

[0012]FIG. 7 is a diagram of a revolution speed of the turbine, atemperature of an exhaust gas, a quantity of fuel supply per unit time,and a current supply per unit time to a motor of an another conventionalgas turbine apparatus during an igniting operation, each illustrated asa function of an elapsed time. In FIG. 7, NR (Number of Revolution)represents a revolution speed of the turbine, FCV (Fuel Control Valve)represents an opening of the fuel flow control valve, EGT (Exhaust GasTemperature) represents a temperature of the exhaust gas, and MC (MotorCurrent) represents a quantity of current supply per unit time to themotor, respectively.

[0013] In this conventional gas turbine apparatus, first of all, theturbine is rotatively driven by the motor, and as shown in FIG. 7, afterthe revolution speed of the turbine reaches up to a certain revolutionspeed NR1 allowing for ignition, this revolution speed is maintained.Then, the fuel flow control valve is opened to start a fuel supply (t₁)to the combustor, and the quantity of fuel supply per unit time isincreased gradually. In synchronism with the starting of the fuelsupply, the igniting operation on the mixture of fuel and air producedin the combustor is started, and when the air-fuel mixture is ignited(t₂), the mixture is burned to generate the combustion gas.

[0014] After the air-fuel mixture is ignited and the combustion gas isgenerated, the combustion gas is fed to the turbine and thereby theturbine is rotatively driven by the combustion gas and the motor.Subsequently, the current supply to the motor is stopped (t₃), and afterthat, the turbine is rotatively driven only by the combustion gas fedthereto. Further, after the air-fuel mixture is ignited and thecombustion gas supply has been started (t₂˜), a speed up control isapplied in which the opening of the fuel flow control valve iscontrolled to increase the revolution of the turbine at a predeterminedtarget acceleration (ACCsp).

[0015] However, in this conventional gas turbine apparatus, like theconventional apparatus shown in FIGS. 5 and 6, immediately after thespeed up control has been applied (t₂), as shown in FIG. 7, the quantityof fuel supply per unit time is temporarily increased due to the speedup control to quickly raise the acceleration of revolution of theturbine from zero to the target acceleration (ACCsp) (see FCV in FIG.7). Accordingly, the exhaust gas temperature also rises up rapidly, andthereby the temperature of the gas turbine apparatus, in particular ofthe combustor thereof rises up quickly up to high temperature whichcould result in a serious damage thereof (see EGT of FIG. 7).

[0016] On the other hand, after the rotative driving for the turbine bythe motor has been stopped, the turbine is required to increase therevolution speed only by the combustion gas fed thereto. This mightcause the additional problem that, right after the rotative driving bythe motor has been stopped (t₃), the quantity of fuel supply per unittime is increased by a control action to maintain the targetacceleration, which could result in a further temperature rise of thegas turbine apparatus.

SUMMERY OF THE INVENTION

[0017] The present invention has been made in the light of theproblematic circumstances described above and the object thereof is toprovide a gas turbine apparatus and a starting method thereof, whichimproves a reliability in starting operation by making it possible toensure the ignition of the air-fuel mixture under various conditions,and further makes it possible to depress the temperature rise of the gasturbine, which may otherwise occurs immediately after the ignition.

[0018] Another object of the present invention is to provide a gasturbine apparatus which makes it possible to depress the rapidtemperature rise of the gas turbine apparatus during the ignitingoperation by preventing a rapid increase of the quantity of fuel supplyprovided for the combustion.

[0019] In order to solve the problem described above, according to afirst aspect of the present invention, there is provided an innovativestarting method of a gas turbine apparatus comprising the steps ofrotatively driving a turbine by a motor coupled to the turbine, while atthe same time supplying a compressed air to a combustor by an aircompressor operating in interlocking motion with the turbine, starting afuel supply to the combustor when a revolution speed of the turbine hasreached up to a predetermined value, and simultaneously starting anigniting operation on an air-fuel mixture in the combustor, the methodcharacterized in that at least during the igniting operation to theair-fuel mixture in the combustor, a quantity of fuel supply per unittime to the combustor is increased while increasing the revolution speedof the turbine.

[0020] According to a second aspect of the present invention, there isprovided an innovative gas turbine apparatus comprising a motor forrotatively driving a turbine, a motor control section for controlling arevolution speed of the motor, a combustor for burning an air-fuelmixture thereby generating a combustion gas therein, an air compressorfor supplying a compressed air to said combustor, the compressoroperating in interlocking motion with the turbine, and a fuel flowcontrol valve for controlling a quantity of fuel supply per unit time tothe combustor, the apparatus characterized in that at least during theigniting operation to the air-fuel mixture in the combustor, a quantityof fuel supply per unit time to the combustor is increased through thefuel flow control valve while increasing the revolution speed of theturbine by said motor control section by the use of the motor.

[0021] According to the first and second aspect of the presentinvention, since the air fuel ratio can be controlled to follow thechange in the suitable ignition condition, it can be ensured to performthe igniting operation without any failure. Further, since the turbinehas been accelerated to some extent when it is ignited, the deviation ofthe acceleration of revolution of the turbine at the point of ignitionfrom the target acceleration thereof may be made small. Accordingly, anexcessive supply of the fuel immediately after the ignition followed bythe shifting to the speed up control phase can be avoided therebypreventing an excessive temperature rise in the gas turbine apparatus,which otherwise might occur right after the ignition.

[0022] According to a third aspect of the present invention, there isprovided an innovative starting method of a gas turbine apparatuscomprising the steps of igniting a mixture of fuel and air whilerotatively driving a turbine by a motor, to combust the mixture, andsupplying a combustion gas generated by the combustion to the turbinethereby increasing a revolution speed of the turbine, the methodcharacterized in that for a predetermined time period after the mixturehas been ignited, a quantity of fuel supply per unit time provided forthe combustion is held to be constant.

[0023] According to the third aspect of the present invention, since thequantity of fuel supply per unit time is held constant for a certaintime period after the air-fuel mixture is ignited, an excessive fuelsupply can be prevented, which otherwise might occur immediately afterthe ignition. Consequently, the rapid temperature rise of the gasturbine apparatus could be prevented.

[0024] Further, according to a preferred embodiment of the third aspect,after the predetermined time period has elapsed, the quantity of fuelsupply per unit time is gradually increased while at the same time, therotative driving force for the turbine provided by the motor isdecreased gradually.

[0025] According to the third aspect of the present invention, after arotative driving mode of the turbine is gradually shifted from a drivingphase by the motor to a driving phase by the combustion gas, therotative driving of the turbine by the motor is stopped. As a result,since upon stopping the rotative driving by the motor, a control actionfor supplying the additional fuel to maintain the target accelerationcan be relaxed, an excessive fuel supply may be depressed therebypreventing the rapid temperature rise of the gas turbine apparatus.

[0026] Further, if the revolution speed of the turbine increases whileholding the quantity of fuel supply per unit time to be constant afterthe ignition, only the quantity of the air supplied into the combustorincreases, which results in a drop of the ratio of the fuel to the airin the mixture produced in the combustor. This could cause sometimes aspecific phenomenon referred to as a flame-out where a combustion flamegoes out. According to the preferred embodiment of the third aspect,since the quantity of fuel supply per unit time is once held constantand then increased gradually, the rapid temperature rise of the gasturbine apparatus can be avoided while preventing the flame-outphenomenon from occurring.

[0027] According to a fourth aspect of the present invention, there isprovided an innovative gas turbine apparatus in which a mixture of airand fuel is combusted and a combustion gas generated by the combustionis supplied to a turbine to rotatively drive the turbine, the apparatuscharacterized in comprising an ignition means for performing an ignitingoperation on the air-fuel mixture while rotatively driving the turbineby a motor during starting operation, a fuel flow control valve ofvariable opening for controlling a quantity of fuel supply to beprovided for the combustion, an ignition detecting means for detectingan ignition of the air-fuel mixture; and an opening holding means forholding the opening of the fuel flow control valve to be constant for apredetermined time period after the ignition of the air-fuel mixture hasbeen detected by the ignition detecting means.

[0028] According to a preferred embodiment of the fourth aspect, theinnovative gas turbine apparatus further comprises a driving forcecontrolling means for gradually decreasing a current supply per unittime to the motor and at the same time gradually increasing the openingof the fuel flow control valve after the predetermined time period haselapsed.

[0029] In this case, it is preferable that the driving force controllingmeans comprises an air fuel ratio control section for controlling an airfuel ratio of a mixture by operating the opening of the fuel flowcontrol valve, and a current supply control section for controlling thecurrent supply per unit time to the motor, wherein after thepredetermined time period has elapsed, the opening of said fuel flowcontrol valve is gradually increased by the air fuel ratio controlsection while controlling the motor by the current supply controlsection such that the turbine may keep a predetermined targetacceleration of revolution.

[0030] Alternatively, it is also preferable that the driving forcecontrolling means comprises a current supply control section forcontrolling the current supply per unit time to the motor, and anacceleration control section for controlling an acceleration ofrevolution of the turbine by operating the opening of the fuel flowcontrol valve, wherein after the predetermined time period has elapsed,the current supply per unit time to the motor is gradually decreased bythe current supply control section while controlling the turbine to keepthe predetermined target acceleration of revolution by the accelerationcontrol section.

[0031] The above and other objects, features and advantages of thepresent invention will become more apparent from the followingdescription when taken in conjunction with the accompanying drawings inwhich preferred embodiments of the present invention are shown by way ofillustrative examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a schematic diagram illustrating a general configurationof a gas turbine apparatus according to an embodiment of the presentinvention;

[0033]FIG. 2 is a diagram of a revolution speed of a turbine, an openingof a fuel flow control valve, and a temperature of an exhaust gas of agas turbine apparatus during an igniting operation, each illustrated asa function of an elapsed time, according to an embodiment of the presentinvention;

[0034]FIG. 3 is a schematic diagram illustrating a general configurationof a gas turbine apparatus according to an another embodiment of thepresent invention;

[0035]FIG. 4 is a diagram of a revolution speed of a turbine, a quantityof fuel supply per unit time, a temperature of an exhaust gas and acurrent supply per unit time to a motor of a gas turbine apparatusduring an igniting operation, each illustrated as a function of anelapsed time, according to the another embodiment of the presentinvention;

[0036]FIG. 5 is a diagram of a revolution speed of a turbine, an openingof a fuel flow control valve, and a temperature of an exhaust gas of aconventional gas turbine apparatus during an igniting operation thereof,each illustrated as a function of an elapsed time;

[0037]FIG. 6 is a diagram of a revolution speed of a turbine, an openingof a fuel flow control valve, and a temperature of an exhaust gas ofanother conventional gas turbine apparatus during an igniting operationthereof, each illustrated as a function of an elapsed time; and

[0038]FIG. 7 is a diagram of a revolution speed of a turbine, a quantityof fuel supply per unit time, a temperature of an exhaust gas and acurrent supply per unit time to a motor of a still further conventionalgas turbine apparatus during an igniting operation thereof, eachillustrated as a function of an elapsed time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0039] Preferred embodiments of the present invention will now bedescribed with reference to the attached drawings.

[0040]FIG. 1 is a schematic diagram illustrating a general configurationof a gas turbine apparatus according to an embodiment of the presentinvention.

[0041] As shown in FIG. 1, the gas turbine apparatus according to theembodiment of the present invention comprises a turbine 1, a combustor 2for supplying a combustion gas to the turbine 1, a fuel flow controlvalve 19 for controlling a quantity of fuel supply per unit time to thecombustor 2, an air compressor 3 for supplying a compressed air to thecombustor 2, and a turbine control section 11 for controlling theturbine 1.

[0042] The turbine 1 is equipped with a plurality of rotary vanes (notshown) for receiving a fluid for rotation, and rotatably supported via arotary shaft 6 in a casing (not shown). The air compressor 3 is drivenby the turbine 1 via the rotary shaft 6 so as to compress the air. Theair compressor 3 is connected to the combustor 2 via a piping 7, so thatthe air compressed by the air compressor 3 is supplied to the combustor2 through the piping 7.

[0043] The fuel flow control valve 19 is disposed upstream to thecombustor 2, and the fuel supplied from a fuel supply source, though notshown, passes through the fuel flow control valve 19 and then enters thecombustor 2. The fuel flow control valve 19 is configured to be of avariable opening type, such that the quantity of fuel supply to thecombustor 2 may be controlled by operating the opening thereof. It is tobe noted that the turbine control section 11 controls the turbine 1 byoperating the opening of the fuel flow control valve 19 so that anacceleration of revolution of the turbine 1 may approach to a targetacceleration.

[0044] The fuel and the compressed air supplied to the combustor 2together produce an air-fuel mixture in the combustor 2, where theair-fuel mixture is burned to generate a combustion gas of hightemperature and high pressure. Then, the combustion gas is supplied tothe gas turbine 1 to revolve it at high revolution speed. A revolutionspeed detecting section 12 for detecting a revolution speed of theturbine 1 is installed on the rotary shaft 6 at a position near to aterminal end thereof located in the motor 5 side.

[0045] The gas turbine apparatus according to this embodiment furthercomprises the motor 5 coupled to the rotary shaft 6 and a motor controlsection 8 for controlling a revolution speed of the motor 5, as shown inFIG. 1. In this embodiment, the motor 5 functions as a starting motorfor the gas turbine apparatus, wherein the motor control section 8controls the revolution speed of the motor 5.

[0046]FIG. 2 is a diagram of the revolution speed of the turbine(NR),the opening of the fuel flow control valve(FCV), and a temperature of anexhaust gas(EGT) of the gas turbine apparatus of the present embodimentduring the igniting operation, each illustrated as a function of anelapsed time.

[0047] As shown in FIG. 2, when the gas turbine apparatus is to bestarted, first of all, an electric power is supplied to the motor 5 sothat the turbine 1 may be rotatively driven by the motor 5 (see thedotted line MC in FIG. 2). After the revolution speed of the turbine 1has reached up to a certain revolution speed suitable for ignition(NR,), the motor 5 is controlled by the motor control section 8 suchthat the revolution speed of the turbine 1 may be increased gradually.At that time, since the motor 5 and the air compressor 3 are interlockedwith each other through the rotary shaft 6, the quantity of thecompressed air supply to the combustor 2 is also increased gradually.

[0048] Almost in synchronism with the starting of increase in therevolution speed of the turbine 1 by the motor control section 8, thefuel flow control valve 19 is opened to start a fuel supply to thecombustor 2 (t₁). Further, upon starting the fuel supply to thecombustor 2, the fuel flow control valve 19 is controlled to increaseits opening gradually to increase the quantity of the fuel supply to thecombustor 2.

[0049] In the combustor 2, the mixture is produced by the compressed airand the fuel, and the igniting operation on this air-fuel mixture isstarted almost in synchronism with the starting of the fuel supply tothe combustor 2. Although the air fuel ratio of the mixture suitable forthe ignition varies depending on conditions such as the temperature ofthe gas turbine main body, while during the igniting operation beingperformed (between t₁ and t₂), the actual air fuel ratio will vary sincethe quantities of the compressed air supply and the fuel supply to thecombustor 2 both increase as described above. Accordingly, the air-fuelmixture is ignited when the air fuel ratio reaches a certain valuematching the condition suitable for the ignition at that time.

[0050] After the igniting operation on the air-fuel mixture completed,the combustion gas is supplied to the turbine 1, which obtains a drivingforce from the combustion gas to increase its revolution speed. Afterthe rotative driving of the turbine 1 by the combustion gas started(after t₂), the control mode is shifted to the speed up control phase bythe turbine control section 11. It is to be noted that whether or notthe igniting operation on the air-fuel mixture in the combustor 2 havingbeen completed is determined by measuring the exhaust gas temperaturewith an exhaust gas temperature measuring device 17 installed on thepiping.

[0051] Immediately after the control mode has been shifted to the speedup control phase, since the turbine 1 has been accelerated by the motor5 to some extent as shown in FIG. 2, the deviation of the accelerationof revolution of the turbine 1 from the target acceleration thereof issmall at this point. Accordingly, as shown in FIG. 2, the fuel flowcontrol valve 19 is not required to open its opening excessively tobring the acceleration of revolution of the turbine 1 close to thetarget acceleration, and as a result, an excessive fuel supply to thecombustor 2 can be avoided thereby preventing an excessive temperaturerise in the gas turbine apparatus, which otherwise might occur rightafter the ignition.

[0052]FIG. 3 is a schematic diagram illustrating a general configurationof the gas turbine apparatus according to a second embodiment of thepresent invention.

[0053] As shown in FIG. 3, the gas turbine apparatus according to thisembodiment essentially comprises a turbine 1, a combustor 2 forcombusting a mixture of fuel and air, a fuel flow control valve 19 forcontrolling a quantity of fuel supply to the combustor 2, and an aircompressor 3 which operates in interlocking motion with the turbine 1for supplying a compressed air to the combustor 2, like theaforementioned embodiment.

[0054] The turbine 1 is equipped with a plurality of rotary vanes (notshown) for receiving a fluid for rotation, and rotatably supported via arotary shaft 6 in a casing(not shown). The air compressor 3 is driven bythe turbine 1 via the rotary shaft 6 so as to compress the air. The aircompressor 3 is connected to the combustor 2 via a piping 7, so that theair compressed by the air compressor 3 is supplied to the combustor 2through the piping 7.

[0055] The fuel flow control valve 19 is disposed upstream to thecombustor 2, and the fuel supplied from a fuel supply source, though notshown, passes through the fuel flow control valve 19 and enters thecombustor 2. The fuel flow control valve 19 is configured to be of avariable opening type, such that the quantity of fuel supply to thecombustor 2 may be controlled by operating the opening thereof.

[0056] The fuel and the air supplied to the combustor 2 together producean air-fuel mixture in the combustor 2, where the air-fuel mixture isburned to generate a combustion gas of high temperature and highpressure. Then, the combustion gas is supplied to the gas turbine 1 torevolve it at high revolution speed. A revolution speed of the turbine 1is detected by a revolution speed detecting section 12 installed on therotary shaft 6 at a location near to a terminal end thereof, and therevolution speed of the turbine 1 detected by the revolution speeddetecting section 12 is sent to an acceleration control section 11′.

[0057] The acceleration control section 11′ calculates an accelerationof revolution of the turbine 1 by differentiating the revolution speedof the turbine 1 sent from the revolution speed detecting section 12,and controls the acceleration of revolution of the turbine 1 byoperating the opening of the fuel flow control valve 19 so that thecalculated acceleration may approach a target acceleration.

[0058] A generator 5 is coupled with the rotary shaft 6 at a locationnear to the terminal end thereof, through which the generator 5 isrotatively driven by the turbine 1 to generate electricity. It is to benoted that in this embodiment, the generator 5 is used as a startingmotor during the starting operation. Accordingly, the generator will besometimes referred to as a motor in the following description.

[0059] The gas turbine apparatus according to this embodiment furthercomprises an ignition means for performing an igniting operation on theair-fuel mixture while rotatively driving the turbine 1 by the motor 5during the starting operation, an ignition detecting means 22 fordetecting the ignition of the air-fuel mixture, an air fuel ratiocontrol section 15 for controlling a ratio between air and fuel in theair-fuel mixture by operating the opening of the fuel flow control valve19, a current supply control section 16 for controlling a current supplyper unit time to the motor 5.

[0060] In the present embodiment, the ignition means designates anignition plug (not shown) installed within the combustor 2. Further, theignition detecting means 22 of the present embodiment comprises anexhaust gas temperature sensor 20 for measuring a temperature of thecombustion gas after having been supplied to the turbine 1, and anignition determining section 21 for determining the ignition of themixture when the exhaust gas temperature measured by the exhaust gastemperature sensor 20 indicates a predetermined rising rate.

[0061] The air fuel ratio control section 15 is designed to hold theopening of the fuel flow control valve 19 to be constant for apredetermined time period after the detection of the ignition of theair-fuel mixture by the ignition detecting means 22. That is, the airfuel ratio control section 15 functions as a means for holding theopening (hereafter referred to as an opening holding means). Further,the air fuel ratio control section 15 is designed to gradually increasethe opening of the fuel flow control valve 19 after the abovepredetermined time period has elapsed.

[0062] The current supply control section 16 makes it possible for theturbine 1 to be controlled to a desired revolution speed and/oracceleration during the starting operation by controlling the currentsupply per unit time to the motor 5. The current supply control section16 is designed such that the turbine 1 may be held at a predeterminedrevolution speed suitable for the ignition during the ignition meansperforming the igniting operation on the air-fuel mixture, and furtherdesigned such that the revolution of the turbine 1 may be increased at apredetermined target acceleration while the quantity of fuel supply perunit time is held constant by the air fuel ratio control section 15after the ignition of the air-fuel mixture.

[0063] According to the air fuel ratio control section 15 and thecurrent supply control section 16 configured as described above, afterthe quantity of fuel supply per unit time has been held constant for thepredetermined time period following the ignition of the air-fuelmixture, since the quantity of fuel supply per unit time is graduallyincreased by the air fuel ratio control section 15, then a rotativedriving force of the turbine 1 by the combustion gas is increased. Atthat time, since the current supply control section 16 controls thecurrent supply per unit time to the motor 5 such that the revolution ofthe turbine 1 may increase at a target acceleration, the current supplyper unit time to the motor 5 is decreased in synchronism with theincrease of the rotative driving force provided by the combustion gas.

[0064] That is, when the acceleration of revolution of the turbine 1 isheld constant via the motor 5, if the rotative driving force for theturbine 1 provided by the combustion gas increases, in synchronismtherewith, the rotative driving force for the turbine 1 provided by themotor 5 decreases. Accordingly, in the present embodiment, the drivingforce control means is composed of the air fuel ratio control means 15and the current supply control section 16.

[0065] An operation of the opening holding means and the driving forcecontrol means will now be described with reference to FIG. 4. FIG. 4 isa diagram of the revolution speed of the turbine, the quantity of fuelsupply per unit time, the exhaust gas temperature and the current supplyper unit time to the motor of the gas turbine apparatus of theembodiment shown in FIG. 3 during the igniting operation, eachillustrated as a function of the elapsed time. In FIG. 4, NR representsthe revolution speed of the turbine 1, FCV the opening of the fuel flowcontrol valve 19, EGT the exhaust gas temperature, and MC the currentsupply per unit time to the motor 5, respectively. As comparison, thosefor the conventional gas turbine apparatus shown in FIG.7 are shown bydotted lines.

[0066] As shown in FIG. 4, first of all, the turbine 1 is rotativelydriven by the motor 5, and when the revolution speed of the turbine 1reaches up to a certain value NR1 suitable for the ignition, thisrevolution speed is maintained under a control of the current supplycontrol section 16. Then the fuel flow control valve 19 is opened tostart a fuel supply (t₁), and the fuel is supplied to the combustor 2while gradually increasing a quantity of fuel supply per unit time. Insynchronism with starting of the fuel supply, the igniting operation isstarted by the ignition means in the combustor 2.

[0067] When the air-fuel mixture is ignited (t₂), the air-fuel mixtureis combusted to generate the combustion gas, and consequently therevolution speed of the turbine 1 is increased since in addition to themotor, the combustion gas also provides a driving force to the turbine1. When the air-fuel mixture is ignited, the exhaust gas temperaturerises, and so the completion of the igniting operation to the air-fuelmixture is detected by the ignition detecting means 22.

[0068] When the ignition of the air-fuel mixture is detected by theignition detecting means 22, for a predetermined time period startingfrom this detection time (from t₂ to t₃), the opening of the fuel flowcontrol valve 19 is controlled to be constant by the air fuel ratiocontrol section 15 and thereby the quantity of fuel supply per unit timeto the combustor 2 is kept constant (see FCV in FIG. 4). In prior artshown in FIG. 7, however, the acceleration control section 11′ applies aspeed up control mode right after the ignition and thereby the exhaustgas temperature rises up rapidly as shown by a dotted line in FIG. 4,but in the present embodiment, the excessive temperature rise in theexhaust gas can be avoided since the quantity of fuel supply per unittime provided for the combustion by the air fuel ratio control section15 is held constant.

[0069] After the ignition of the air-fuel mixture ha been detected bythe ignition detecting section 22, the turbine 1 will receive thedriving force from both of the combustion gas and the motor 5 toincrease the revolution speed thereof. At that time, the current supplycontrol section 16 controls the motor 5 such that the revolution of theturbine 1 may increase with the predetermined target acceleration(ACCsp). This allows the revolution of the turbine 1 to increase withthe target acceleration (ACCsp) even while the opening of the fuel flowcontrol valve is held constant.

[0070] After the opening of the fuel flow control valve 19 held constantfor the predetermined time period, then the air fuel ratio controlsection 15 controls the fuel flow control valve 19 such that the openingthereof may increase gradually with a predetermined increasing rate(t₃˜). Consequently, the rotative driving force for the turbine providedby the motor 5, or the current supply per unit time to the motor 5, isgradually decreased (see MC in FIG. 4) since the current supply controlsection 16 controls the revolution of the turbine 1 to be held at thepredetermined acceleration, as described above. That is, as the rotativedriving force by the combustion gas is increased by increasing theopening of the fuel flow control valve 19, the current supply per unittime to the motor 5 is automatically decreased to reduce the rotativedriving force by the motor 5.

[0071] When the current supply per unit time to the motor 5 is decreasedand the quantity of fuel supply per unit time provided for thecombustion is increased to some extent, the current supply to the motoris stopped completely (t₄). Under this condition, the turbine 1 isrequired to increase its revolution speed only by the combustion gassupplied therefor. After the current supply to the motor 5 has droppedto zero, a main controller for the apparatus is switched from the airfuel ratio control section 15 to the acceleration control section 11′,which applies thereafter the speed up control to the turbine 1.

[0072] In this embodiment, the excessive supply of the fuel to thecombustor 2, which otherwise might occur immediately after the currentsupply to the motor 5 having been stopped completely, can be avoided bygradually shifting the driving mode of the turbine 1 from that by themotor 5 to that by the combustion gas before stopping the current supplyto the motor 5. Further, if the quantity of fuel supply per unit timeprovided for the combustion is held constant while increasing therevolution of the turbine 1 after the ignition of the air-fuel mixture,the ratio of the fuel quantity to the air quantity in the mixture drops,which may sometimes lead to the flame out. In the present embodiment,however, since the quantity of fuel supply per unit time is once heldconstant after the ignition and then increased gradually, the rapidtemperature rise of the gas turbine apparatus can be avoided whilepreventing the flame-out from occurring.

[0073] Next, a third embodiment of the present invention will bedescribed.

[0074] General configuration of the gas turbine apparatus according tothe third embodiment is completely similar to that of the secondembodiment. Further, in the present embodiment, the behaviors of therevolution speed of the turbine, the quantity of fuel supply per unittime, the exhaust gas temperature and the current supply per unit timeto the motor of the gas turbine apparatus observed during the startingoperation are similar to those in the second embodiment. Therefore, theconfiguration and the action of the present embodiment accompanied withno specific descriptions therefor are similar to those of the secondembodiment, and the description thereof will be omitted.

[0075] The third embodiment is similar to the second embodiment in thepoint that the air fuel ratio control section 15 is provided as theopening holding means for the fuel flow control valve 19. A differenceof the present embodiment from the second embodiment is that the formerhas a different driving force controlling means for gradually decreasinga current supply per unit time to the motor 5 while increasing thequantity of fuel supply per unit time. That is, in the presentembodiment, the driving force control means comprises the current supplycontrol section 16 and the acceleration control section 11′.

[0076] In the third embodiment, after the quantity of fuel supply perunit time is held constant for a predetermined time period by the airfuel control section 15, the current supply per unit time to the motor 5is gradually decreased by the current supply control section 16 whileholding the revolution of the turbine to be at a predetermined targetacceleration by the acceleration control section 11′. When the currentsupply per unit time is decreased by the current supply control section16, the rotative driving force for the turbine 1 provided by the motor 5is reduced. In response to this, the acceleration control section 11′controls the fuel flow control valve 19 to increase the opening thereofand thereby to increase the rotative driving force provided by thecombustion gas in order to keep the target acceleration of revolution ofthe turbine 1.

[0077] That is, under the condition where the acceleration of revolutionof the turbine 1 is held constant by the acceleration control section11′, if the current supply per unit time to the motor 5 is decreased,the quantity of fuel supply per unit time provided for the combustion isincreased by the acceleration control section 11′. As a result, thecurrent supply per unit time to the motor 5 and the opening of the fuelflow control valve 19 show the same behaviors with those of the secondembodiment described above.

[0078] Thus, though the present embodiment is different from the secondembodiment in the driving force controlling means, the behaviors of thequantity of fuel supply per unit time to the combustor 2 and the currentsupply per unit time to the motor 5 observed during the ignitingoperation are quite the same with those of the second embodiment.Therefore, the present embodiment, similar to the second embodiment, candepress the rapid temperature rise of the gas turbine apparatus whilepreventing the flame-out from occurring during the igniting operation.

[0079] It should be appreciated that the gas turbine apparatus of thepresent invention is not limited to those described in the aboveembodiments, but may be modified in various manners without departingfrom the spirit and the scope of the present invention.

[0080] As having been described above, according to the presentinvention, since the air fuel ratio can be controlled to follow thechange in the suitable ignition condition, it can be ensured to performthe igniting operation without any failure. Further, in the firstembodiment, since the turbine has been accelerated to some extent whenit is ignited, the deviation of the acceleration of revolution of theturbine at the point of ignition from the target acceleration thereof issmall. Accordingly, an excessive supply of the fuel immediately afterthe ignition can be avoided thereby preventing an excessive temperaturerise in the gas turbine apparatus, which otherwise might occur rightafter the ignition.

[0081] Also, in the second embodiment, by holding the quantity of fuelsupply per unit time constant for a certain period after the air-fuelmixture is ignited, the excessive fuel supply can be prevented, whichotherwise might occur immediately after the ignition. Consequently, therapid temperature rise of the gas turbine apparatus could be prevented.

[0082] Further, by stopping the rotative driving of the turbine by themotor after the rotative driving mode of the turbine is graduallyshifted from the driving phase by the motor to the driving phase by thecombustion gas, upon stopping the rotative driving by the motor, thecontrol action for supplying the additional fuel to maintain the targetacceleration can be relaxed. Accordingly, the excessive fuel supply maybe depressed thereby preventing the rapid temperature rise of the gasturbine apparatus.

[0083] Still further, by once holding the quantity of fuel supply perunit time constant and then increasing it gradually, the rapidtemperature rise of the gas turbine apparatus can be avoided whilepreventing the flame-out from occurring.

1. A starting method of a gas turbine apparatus comprising the steps of:rotatively driving a turbine by a motor coupled to said turbine, whileat the same time supplying a compressed air to a combustor by an aircompressor operating in interlocking motion with said turbine; startinga fuel supply to said combustor when a revolution speed of said turbinehas reached up to a predetermined value; and simultaneously starting anigniting operation on an air-fuel mixture in said combustor; wherein atleast during the igniting operation to the air-fuel mixture in saidcombustor, a quantity of fuel supply per unit time to said combustor isincreased while increasing the revolution speed of said turbine.
 2. Agas turbine apparatus comprising: a motor for rotatively driving aturbine; a motor control section for controlling a revolution speed ofsaid motor; a combustor for burning an air-fuel mixture therebygenerating a combustion gas therein; an air compressor for supplying acompressed air to said combustor, said compressor operating ininterlocking motion with said turbine; and a fuel flow control valve forcontrolling a quantity of fuel supply per unit time to said combustor;wherein at least during an igniting operation to the air-fuel mixture insaid combustor, a quantity of fuel supply per unit time to saidcombustor is increased through said fuel flow control valve whileincreasing a revolution speed of said turbine by said motor throughcontrol of said motor control section.
 3. A starting method of a gasturbine apparatus comprising the steps of: igniting a mixture of fueland air while rotatively driving a turbine by a motor, to combust saidmixture; and supplying a combustion gas generated by said combustion tosaid turbine thereby increasing a revolution speed of said turbine;wherein for a predetermined time period after the mixture has beenignited, a quantity of fuel supply per unit time provided for thecombustion is held to be constant.
 4. A starting method of a gas turbineapparatus in accordance with claim 3, in which after said predeterminedtime period has elapsed, the quantity of fuel supply per unit time isgradually increased while at the same time, a rotative driving force forsaid turbine provided by said motor is decreased gradually.
 5. A gasturbine apparatus in which a mixture of air and fuel is combusted and acombustion gas generated by said combustion is supplied to a turbine torotatively drive said turbine, said apparatus comprising: an ignitionmeans for performing an igniting operation on the air-fuel mixture whilerotatively driving said turbine by a motor during starting operation; afuel flow control valve of variable opening for controlling a quantityof fuel supply per unit time to be provided for the combustion; anignition detecting means for detecting an ignition of the air-fuelmixture; and an opening holding means for holding the opening of saidfuel flow control valve to be constant for a predetermined time periodafter the ignition of the air-fuel mixture has been detected by saidignition detecting means.
 6. A gas turbine apparatus in accordance withclaim 5, said apparatus further comprising a driving force controllingmeans for gradually decreasing a current supply per unit time to saidmotor and at the same time gradually increasing the opening of said fuelflow control valve after said predetermined time period has elapsed. 7.A gas turbine apparatus in accordance with claim 6, in which saiddriving force controlling means comprises: an air fuel ratio controlsection for controlling an air fuel ratio of a mixture by operating theopening of said fuel flow control valve; and a current supply controlsection for controlling the current supply per unit time to said motor;wherein after said predetermined time period has elapsed, the opening ofsaid fuel flow control valve is gradually increased by said air fuelratio control section while controlling said motor by said currentsupply control section such that said turbine may keep a predeterminedtarget acceleration of revolution.
 8. A gas turbine apparatus inaccordance with claim 6, in which said driving force controlling meanscomprises: a current supply control section for controlling the currentsupply per unit time to said motor; and an acceleration control sectionfor controlling an acceleration of revolution of said turbine byoperating the opening of said fuel flow control valve; wherein aftersaid predetermined time period has elapsed, the current supply per unittime to said motor is gradually decreased by said current supply controlsection while controlling said turbine to keep the predetermined targetacceleration of revolution by said acceleration control section.